javascript - return value from asynchronous function in Nodejs -

i using nodejs query data mongodb throught mongoose. after data, want on data before responding client. can not return-value. after looking on google, have learned node.js functions asynchronous javascript function (non i/o blocking). try tut (http://www.youtube.com/watch?v=xdw9bk-9pny) not work. below code. myobject valued inside "find()" function , undefined outside "find()" function. should data? thanks!

var person = mongoose.model('person', personschema); var product = mongoose.model('product', productschema); var myobject = new object();  person.find().exec(function (err, docs) {     (var i=0;i<docs.length;i++)     {      product.find({ user: docs[i]._id},function (err, pers) {     myobject[i] = pers;     console.log(myobject[i]); //return value ok     });     console.log(myobject[i]); //return undefined value     }     console.log(myobject); //return undefined value });     console.log(myobject); //return undefined value  app.listen(3000); console.log('listening on port 3000'); 

the reason you're getting undefined values because find function asynchronous, , can finish @ time. in case, finishing after you're using console.log(), values undefined when you're accessing them.

to fix problem, can use values inside find function's callback. this:

var person = mongoose.model('person', personschema); var product = mongoose.model('product', productschema); var myobject = new object();  function getdata(docs, callback) {   function loop(i) {     product.find({ user: docs[i]._id}, function (err, pers) {       myobject[i] = pers;        if (i < docs.length) {         loop(i + 1);       } else {         callback();       }     });   };   loop(0); };  person.find().exec(function(err, docs) {   getdata(docs, function() {     // myobject has been populated @ point   }); }); 

the data processing has been moved loop waits previous iteration complete. way, can determine when last callback has fired in order fire callback in wrapper function.